Zhou Yongkang has been under investigation since July. Photograph: Jason Lee/Reuters

China’s Communist party expelled its former security tsar, Zhou Yongkang, months after placing him under investigation for “serious disciplinary violations,” the state newswire Xinhua reported just after midnight on Saturday, moving forward China’s highest-level corruption case in recent history.

Members of the standing committee of the politburo, the country’s highest governing body, had decided on Friday to revoke Zhou’s party membership and transfer his case and “relevant clues” to China’s judicial authorities “to deal with them in accordance with the law,” the newswire said.

Zhou, 72, is China’s highest-level official to be prosecuted since the Gang of Four were tried in 1980 for overseeing atrocities during the Cultural Revolution. He is the most senior figure in the party’s history to be investigated for corruption.

“He used his position to give illegal benefits to many people, and took bribes directly and via his family members; abused his position to help his family members, mistresses and friends gain huge profits through business activities at the cost of state assets; leaked party and state secrets; severely breached regulations of corruption by taking a great amount of assets belonging to other people; committed adultery with a number of women, and traded money and power for sexual advantages.”

His actions have “greatly harmed the party’s image”, Xinhua continued, “and have caused great losses to the party and the people”.

State media has made little mention of Zhou since July, when Xinhua announced that he was under violation for “serious disciplinary violations”, shorthand for corruption.

Anti-corruption authorities had been tightening the net around Zhou for months. They detained a large cohort of his one-time aides and proteges, including a former vice-governor of Sichuan province, a state-owned enterprise regulator and a handful of senior officials at China National Petroleum Corporation.

According to a New York Times investigation in April, authorities also targeted Zhou’s “wife, a son, a brother, a sister-in-law, a daughter-in-law and the son’s father-in-law”, all of whom had apparently used Zhou’s political clout for financial gain. Many were in effect disappeared – held at secret locations for months, incommunicado and without trial.

Before Zhou retired in 2012, he spent five years as China’s third most-powerful man – the head of the party’s political and legislative affairs committee, controlling the country’s state security, courts, police and paramilitary. He was known for his frequent use of the term “hostile forces” – an intentionally vague category encompassing a multitude of disparate camps, from pro-democracy campaigners to activists in Tibet – and his relentless campaigns to repress them. Zhou’s only superiors were the president and the prime minister. During his tenure, China’s domestic security budget exceeded that of its military.

China’s president, Xi Jinping, has overseen a sweeping anti-graft campaign since he took power in late 2012, and Zhou has been by far its biggest target. Analysts say that Xi’s campaign against Zhou – one of his strongest rivals in the party – has allowed him to consolidate power, bolstering his ability to push through economic reforms.

Zhou was considered a patron of the disgraced Chongqing party boss Bo Xilai, a one-time presidential hopeful who is serving a life sentence for corruption, embezzlement and abuse of power. In 2012, Bo’s wife murdered a British businessman in a Chongqing hotel, triggering an investigation and his arrest.